In the Paramyxoviridae family, human parainfluenza viruses (HPIV) are RNA viruses included in two genuses of the Paramyxovirinae sub-family:
Respirovirus for type 1 and 3 parainfluenza viruses (HPIV-1, -3);
Rubulavirus for type 2 and 4 parainfluenza viruses (HPIV-2, -4).
HPIVs are envelope viruses. Their genome is approximately 15 kilobases long, constituted by single strand negative polarity RNA. The genome codes for six principal proteins.
The genes NP, P and L respectively code for the nucleoprotein, the phosphoprotein and the polymerase (L stands for large polymerase complex). These three proteins along with the viral RNA form the nucleocapsid (or holonucleocapsid). With the RNA, the nucleoprotein forms a support for the phosphoprotein and the polymerase, allowing transcription and eventually replication of the genome.
The F and HN genes respectively code for the fusion F protein and the haemagglutinin-neuraminidase (HN) protein, which are the two envelope proteins of the viruses and which participate in the mechanism by which the virus enters the host cell.
The HN protein is responsible for attachment of the virus to the cell, by binding itself to cellular sialic acids. Once the virus is attached, the fusion F protein is activated, inserts one of its domains into the cell membrane and then the mechanisms which draw the two membranes together and fuse them are triggered.
HPIVs which have been described in the prior art include various HPIV-2 viruses.
The reference HPIV-2 isolate is the Greer isolate which was isolated from a patient in 1955.
Diagnostic means, which include detecting HPIV-2, are all currently designed using the structure of this reference isolate.
As an example, detecting HPIV-2 in the context of a hospital is currently carried out by isolation in cell culture (on a LLC-MK2 sensitive system) or by immunofluorescence and immunocapture ELISA. The antibodies employed in those techniques were obtained from the HPIV-2 Greer strain.
The inventors have now shown that there is in fact an entire family of HPIV-2 viruses which are sufficiently different from the Greer isolate, and more particularly Greer, Toshiba and V98 isolates, not to be recognized by anti-envelope protein antibodies which are normally used in the prior art to detect HPIV-2.
Similarly, the prior art proposes several techniques for detecting HPIV-2 by PCR, but the primer design is based on the sequence for the Greer isolate, without allowing for the fact that, as the present inventors have shown, there exists an entire family of HPIV-2 viruses which are different from the Greer isolate, and more particularly from Greer, Toshiba and V98 isolates.